New ItemType functions.

ItemType:getClientId() is necessary for OTClient purposes.
Mana drain now counts as damage

This provides a more accurate most damage calculation against vocations
who rely on mana shield.
Pass creature userdata instead of id to onTileCombat
Merge pull request #1060 from conde2/New-ItemType

New ItemType functions.
Merge pull request #3 from otland/master

Merge